This invention relates generally to siliceous minerals such as aluminosilicates and the like, and in particular relates to a method in which said mineral is pretreated to enhance subsequent functionalization, then is caused to react with a functional group-containing variety of an organic compound.
The invention relates specifically to layered silicates of the type which can be represented by the general formula E.sub.i M.sub.x Si.sub.y O.sub.n (OH).sub.m where M is Al, Mg, or Fe, x=2 to 6; y=2 to 8, n=2 to 20, m=0 to 8, and E.sub.i is one or more exchangeable ions (K, Na, Mg, Ca, Ba, Fe, Li, etc.). These layered silicates will hereinafter in this specification be referred to as "layered lattice silicates".
In this disclosure, the term "functionalization" means using a reactant that contains a functional group. The functional group subsists at least to some extent in the product obtained except when an olefin is used which leaves an alkane as product. The term "surface treated" means that only the surface is modified, that is, there is no intercalation in the layered lattice silicate or breakdown of its structure.
In the instance of layered lattice silicates such as kaolin clays, it has long been recognized that products having new properties and uses could be formulated by combining these aluminosilicates with organic materials. However, useful progress in this direction has tended to be limited by the lack of available covalent bonding at the mineral/organic interface. In the past this difficulty has been partially overcome by surface modification of the kaolinite through coupling of organosilane compounds, and subsequent reaction between dependant silanes and organics.
Thus, in Papalos U.S. Pat. No. 3,227,675, for example, kaolin clays are described, the surfaces of which are modified with organofunctional silanes. A typical such agent, e.g., is a methacryloxypropyltrimethoxy silane. The kaolin clays so modified are advantageously used as fillers for natural and synthetic rubbers and the like. It is also pointed out in this patent that such modified products can serve as intermediates for synthesis of new pigments, which are useful as fillers for polymers, elastomers and resins. This result obtains because the silanes used to modify the kaolin clays are di- or polyfunctional, and only one functional group, the silane, is attached to the clay, leaving the remaining reactive groups to react further.
Additional references of this type include Iannicelli U.S. Pat. No. 3,290,165, and Iannicelli U.S. Pat. No. 3,567,680.
However, the modification of aluminosilicates such as kaolin clays by the use of organosilanes, is a complicated and expensive process. Among other things, the cost of the organosilane itself is very high. Furthermore, the resulting products have only limited capability for further reaction, regardless of the particular organosilanes utilized.
It has heretofore been known in addition, that in certain instances high temperature reactions of silicate films with hydrogen can be utilized for certain purposes, such as the production of hydroxide free silica for optical glasses. It is also known to those skilled in the art that products known as "hydrogen clays" can be produced by aqueous reaction of clays with mineral acids, as for example is described in U.S. Pat. No. 3,201,197. Such reactions have substantially no bearing upon the present invention, as will henceforth become evident.
In accordance with the foregoing, it may be regarded as as an object of the present invention, to provide a relatively simple and effective process for forming active intermediates from layered lattice silicates, such as aluminosilicates, which intermediates are eminently capable of subsequent functionalization with organic groups.
The kaolin group of clays represents a crystal structure wherein one gibbsite sheet is condensed with one silica sheet, forming a stable non-expanding type crystal lattice, whereas the remaining two groups, the montmorillonite group and illite group, conform to the expanding crystal lattice, consisting of a gibbsite sheet enclosed between two silica sheets. Clays composed of the non-expanding lattice structures are said to possess moderate surface activity and generally form relatively free flowing systems in water; whereas those composed of the expanding crystal lattice are capable of high colloidal activity and hydration, producing plastic and gel-like water systems.
It is therefore a specific object of the invention to combine kaolin clays with organic materials thereby rendering them lipophilic. That is to say, it is desirable to render normally hydrophilic layered lattice silicates such as kaolin, oleophilic, whereby they may be used as fillers for organic materials such as polymers, elastomers, resins and the like.
It is a yet further object of the present invention, to provide a novel process for preparing analogs of known silane-modified layered lattice silicates, such as analogs of known silane-modified kaolin clays, which process produces such materials with much greater simplicity than prior known techniques for producing the said silane-modified clays.